<body>
  <canvas id="c"></canvas>
</body>
<script type="importmap">
{
  "imports": {
    "three": "../../build/three.module.js",
    "three/addons/": "../../examples/jsm/"
  }
}
</script>

<script type="module">
import * as THREE from 'three';
import { OrbitControls } from 'three/addons/controls/OrbitControls.js';

function main() {

	const canvas = document.querySelector( '#c' );
	const renderer = new THREE.WebGLRenderer( { antialias: true, canvas } );

	const fov = 45;
	const aspect = 2; // the canvas default
	const near = 0.1;
	const far = 10000;
	const camera = new THREE.PerspectiveCamera( fov, aspect, near, far );
	camera.position.set( 0, 1000, 2000 );

	const controls = new OrbitControls( camera, canvas );
	controls.target.set( 0, 5, 0 );
	controls.update();

	const scene = new THREE.Scene();
	scene.background = new THREE.Color( 'black' );

	scene.add( new THREE.GridHelper( 5000, 10 ) );

	let curve;
	let curveObject;
	{

		const controlPoints = [
			[ 1.118281, 5.115846, - 3.681386 ],
			[ 3.948875, 5.115846, - 3.641834 ],
			[ 3.960072, 5.115846, - 0.240352 ],
			[ 3.985447, 5.115846, 4.585005 ],
			[ - 3.793631, 5.115846, 4.585006 ],
			[ - 3.826839, 5.115846, - 14.736200 ],
			[ - 14.542292, 5.115846, - 14.765865 ],
			[ - 14.520929, 5.115846, - 3.627002 ],
			[ - 5.452815, 5.115846, - 3.634418 ],
			[ - 5.467251, 5.115846, 4.549161 ],
			[ - 13.266233, 5.115846, 4.567083 ],
			[ - 13.250067, 5.115846, - 13.499271 ],
			[ 4.081842, 5.115846, - 13.435463 ],
			[ 4.125436, 5.115846, - 5.334928 ],
			[ - 14.521364, 5.115846, - 5.239871 ],
			[ - 14.510466, 5.115846, 5.486727 ],
			[ 5.745666, 5.115846, 5.510492 ],
			[ 5.787942, 5.115846, - 14.728308 ],
			[ - 5.423720, 5.115846, - 14.761919 ],
			[ - 5.373599, 5.115846, - 3.704133 ],
			[ 1.004861, 5.115846, - 3.641834 ],
		];
		const p0 = new THREE.Vector3();
		const p1 = new THREE.Vector3();
		curve = new THREE.CatmullRomCurve3(
			controlPoints.map( ( p, ndx ) => {

				p0.set( ...p );
				p1.set( ...controlPoints[ ( ndx + 1 ) % controlPoints.length ] );
				return [
					( new THREE.Vector3() ).copy( p0 ),
					( new THREE.Vector3() ).lerpVectors( p0, p1, 0.1 ),
					( new THREE.Vector3() ).lerpVectors( p0, p1, 0.9 ),
				];

			} ).flat(),
			true,
		);
		{

			const points = curve.getPoints( 250 );
			const geometry = new THREE.BufferGeometry().setFromPoints( points );
			const material = new THREE.LineBasicMaterial( { color: 0xff0000 } );
			curveObject = new THREE.Line( geometry, material );
			curveObject.scale.set( 100, 100, 100 );
			curveObject.position.y = - 621;
			material.depthTest = false;
			curveObject.renderOrder = 1;
			scene.add( curveObject );

		}

	}

	const geometry = new THREE.BoxGeometry( 100, 100, 300 );
	const material = new THREE.MeshBasicMaterial( { color: 'cyan' } );
	const cars = [];
	for ( let i = 0; i < 10; ++ i ) {

		const mesh = new THREE.Mesh( geometry, material );
		scene.add( mesh );
		cars.push( mesh );

	}

	// create 2 Vector3s we can use for path calculations
	const carPosition = new THREE.Vector3();
	const carTarget = new THREE.Vector3();

	function render( time ) {

		time *= 0.001; // convert to seconds

		{

			const pathTime = time * .01;
			const targetOffset = 0.01;
			cars.forEach( ( car, ndx ) => {

				// a number between 0 and 1 to evenly space the cars
				const u = pathTime + ndx / cars.length;

				// get the first point
				curve.getPointAt( u % 1, carPosition );
				carPosition.applyMatrix4( curveObject.matrixWorld );

				// get a second point slightly further down the curve
				curve.getPointAt( ( u + targetOffset ) % 1, carTarget );
				carTarget.applyMatrix4( curveObject.matrixWorld );

				// put the car at the first point (temporarily)
				car.position.copy( carPosition );
				// point the car the second point
				car.lookAt( carTarget );

				// put the car between the 2 points
				car.position.lerpVectors( carPosition, carTarget, 0.5 );

			} );

		}

		renderer.render( scene, camera );

		requestAnimationFrame( render );

	}

	requestAnimationFrame( render );

}

main();
</script>
